Presently gyroscopes are used in many arrangements, such as inertial platforms and the like, for the measurement of angular velocity. In such arrangements separate gyroscopic instruments are usually used to measure each component of angular velocity. These gyroscopic arrangements are inherently costly and relatively large. Gyroscopes operate by storing a large angular momentum using a flywheel, thus further contributing to their relatively large size. Since the heavy flywheel must be critically balanced, the cost thereof is further increased.
Gyroscopes are further limited in that they cannot withstand a rugged environment because of their relatively delicate bearing and pickoff alignment. For example, I will describe hereinafter apparatus for measuring angular velocity in pitch and yaw of a gun-fired spinning projectile on which such apparatus is mounted. The apparatus undergoes translational acceleration of 20,000 or more g's while being fired from a gun and experiences a large centrifugal acceleration during the measurement due to the spinning of the projectile. This centrifugal acceleration component imposed on such apparatus increases in proportion to the distance away from the spin-axis of the projectile on which the apparatus is mounted and would be very large since space limitations would preclude placing the apparatus near the spin-axis. This centrifugal acceleration can reach 7000 g's on parts of the apparatus which are one inch away from the spin-axis. Furthermore, the gyroscope's angular mounting tolerances would have to be impractically precise.
As in the spinning projectile application two gyroscopes would usually be required, their combines size further precludes their use. Accordingly, another type of rate sensor is required.
Another problem related to kinematics is the calibrating of translational acceleration transducers. Currently, there are four principal methods of calibrating such transducers. These are: (1) static calibration in a centrifuge, (2) calibration versus frequency by rotation in the earth's gravitational field, (3) calibration versus amplitude and frequency on a "shake table" with a precalibrated transducer and (4) calibration versus amplitude and frequency on a "shake table" employing an optical interferometer.
Method (1) is unsatisfactory since it does not provide a dynamic calibration. Method (2), of course, is severely limited because calibrations can only be made up to the .+-.1 g of the earth's gravitational forces and admixes cross-axis sensitivity in varying proportion. Method (3), which is a comparison test performed on a shake table, is accurate to only about 1%, due to practical limitations of current art and, furthermore, this method does not permit the user to locate the physical center of action of the instrument under test. Method (4) is quite cumbersome and is not suitable for routine application.